1. Field of the Invention
The present invention is related to a map displaying method and apparatus, and a navigation system having such a map displaying apparatus. Particularly, the present invention is related to a stereoscopic map displaying method beneficial for the navigation system in which map information is selected from a map database according to a current location of a mobile object such as an automobile, and a perspective map viewing the ground surface along a direction angled to the ground surface is displayed.
2. Description of Related Art
The navigation system is known as an apparatus which assists a driver of an automobile by fetching digital map data stored in storage media such as CD-ROM, displaying a map showing buildings, roads and the like on a display screen, and superposing a current location of the automobile and a direction toward its destination on the map, which are detected by various sensors such as GPS.
A recent navigation system, such as disclosed in Japanese Patent Application Publication (KOKAI) No. 2-244188, uses a pseudo three dimensional display method in which a coordinate transformation of two dimensional map information is executed to generate a pseudo three dimensional image so as to display the map information in the vicinity of the current automobile location in a more easily recognizable manner. The pseudo three dimensional display may give a kind of three dimensional impression to a viewer using the two dimensional map information because, in the pseudo three dimensional display, a view point is set at a predetermined position above the automobile, and a perspective image viewed along a viewing direction which makes an acute angle with respect to the ground plane is displayed.
The pseudo three dimensional display of the prior art is generated from the two dimensional map information using the view point determined while assuming a flat ground surface. This may cause some problems if the stereoscopic map display method mentioned above is executed using three dimensional map information including information regarding a topographical elevation, instead of the two dimensional map information.
Namely, the three dimensional map information contains topographical information such as elevations of mountains, buildings or the like. If such three dimensional information is used and the view point is established with respect to the ground plane at sea level (altitude of 0 m) in the same way as that of the pseudo three dimensional display method, the established view point may end up inside a mountain which protrudes above the ground plane, depending on its height. If that is the case, the navigation system may not be able to display a location of the automobile or carry out the navigation procedure.
The present invention is invented in light of the above mentioned problems, and has an object to provide a map display method and apparatus which enable a stereoscopic map display using three dimensional map data including information indicating horizontal locations of map constituent elements such as topographical features, roads, buildings, and information indicating heights or elevations or altitudes of at least some of the map constituent elements which are located in at least a part of the available horizontal map area.
Another object of the present invention is to provide a navigation system having a stereoscopic map display function which enables renewal of contents of the display smoothly with movement of a vehicle even with the topographic variation or ups and downs of roads.
The above objects of the present invention are accomplished by a map display method in which map information in an area specified in response to a current location of a moving object is read from a map database; a perspective map viewed from a view point toward a ground plane is generated by executing coordinate transformation procedures on the map information; and a scenery image corresponding to the perspective map is displayed on a display device, wherein the view point for generating the perspective map is established above a height of a map constituent element existing at a location specified in response to the current location of the moving object, and the height of the view point is renewed with movement of the moving object.
Further, the above objects of the present invention are accomplished by a map display method in which a perspective map is generated using map information in an area specified in response to a location indicated by input location information, and a scenery image corresponding the perspective map is displayed, wherein a map database which contains the map information includes information regarding heights of map constituent elements existing at least in a part of the available map area; a view point for generating the perspective map is established above a height of a map constituent element existing at a map location specified in response to the location indicated by the input location information when information regarding the height of the constituent element is available; and the height of the view point is reestablished when new input information is provided.
Further, the above objects of the present invention are accomplished by a map display apparatus in which a perspective map is generated from map information in an area specified in response to a location indicated by input location information; and graphic data for displaying a scenery image corresponding the perspective map is outputted; comprising a view point setting unit for establishing at least a height of the view point among variables to be set to generate the perspective map, and a display processing unit for generating the graphic data for displaying the scenery image corresponding the perspective map generated in response to the view point set by the view point setting unit, wherein the view point setting unit establishes a height of the view point above an elevation of a topographical feature at a map location which is specified in response to the location indicated by the input location information when information regarding the elevation of topographical feature is available.
Further, the objects of the present invention are accomplished by a navigation system comprising a map database device, a current location detection device, a map display device for generating a perspective map from map information in an area specified in response to the current location of an automobile, and generating graphic data for displaying a scenery image corresponding the perspective map, and a display device, wherein the map display device comprises a view point setting unit for executing at least a setting procedure of the view point among variables to be set for generating the perspective map, and a display processing unit for generating graphic data for displaying a scenery image corresponding to the perspective map generated in response to the view point established by the view point setting unit, and the view point setting unit establishes a height of the view point above an elevation of a topographical feature at a map location which is specified in response to the detected current location of the automobile when information regarding the elevation of a topographical feature is available.